Create dhclient.conf, set priority for nailgun DNS

When there are couple of DHCP server, nailgun server will be set first resolv.conf

Change-Id: I4077072f38ea445d065e9e49d91a909062529dcf
Closes-bug: 1335210
Merge "Create dhclient.conf, set priority for nailgun DNS" into stable/5.0